With the increasing screen size of the liquid crystal display device, there has been proposed a liquid crystal display device that variably controls a video display area of the liquid crystal panel, in order to achieve power saving and comfortable viewing of the video. When desiring to enjoy a video overflowing with the feeling of being at a live performance, for example, when viewing a sports program or a movie, the viewer causes the video to be displayed on the entire surface of the liquid crystal panel of a large-screen liquid crystal display device. On the other hand, when viewing the other videos, for example, a news commentary program in which a newscaster simply reads a news, the video is displayed as a sub-screen in a restricted video display area of the liquid crystal panel to achieve power saving.
Such a liquid crystal display device uses, as a backlight light source illuminating the liquid crystal panel, a light emitting element such as an LED (Light Emitting Diode) as in an image display device disclosed in Patent Document 1. The image display device disclosed in Patent Document 1 has a so-called local dimming function that, when the video display area of the liquid crystal panel is changed, turns on LEDs of the backlight light source corresponding to a video display area so as to illuminate the changed video display area and turns off LEDs of the backlight light source corresponding to the region outside the video display area.